Isolation trap



FEB. 11, 1969 M, 510mm 3,426,511

ISOLATION TRAP Filed Aug. 31, 1966 OOOO OOOCQDOOOO United States Patent 8 Claims ABSTRACT OF THE DISCLOSURE A non-refrigerated isolation trap for use particularly in conjunction with fluid diffusion pumps in vacuum systerns to prevent backstreaming of vapor from such pumps wherein a tortuous path is provided through the trap. In certain examples, a bed of an anhydrous zeolite compound is positioned in said path.

This application is a continuation-in-part of my earlier application Ser. No. 370,585, filed May 27, 1964, and now abandoned which in turn is a continuation of application Ser. No. 813,720 filed May 18, 1959 and now abandoned.

The present invention relates to isolation traps adapted particularly for use in highly evacuated systems, and more particularly to a high conductance, non-refrigerated isolation trap capable of maintaining isolation under pressure of 1 1O mm. of mercury or less for extended periods.

In the attainment of ultra-high vacua, it is customary to employ vapor diffusion pumps and the like. In vapor diffusion pumps, the mechanism for obtaining a vacuum is momentum transfer from the pump fluid vapor to the gaseous molecules in the system to be evacuated. With such pumps, since a high vapor pressure is required to achieve the pumping action, it is necessary to heat the pump so that the pump fluid becomes vaporized. By providing a high vapor pressure in the pump region, it becomes obvious that as the main system becomes evacuated, the vapor pressure in the pump exceeds the vapor pressure in the system and the difference in vapor pressure causes a back. flow or backstreaming from the pump region to the evacuated region. It is necessary to prevent the pump vapor from backstreaming from the pump to the evacuated region.

To prevent such bac-kstreaming, an isolation trap is conventionally used between the system and the pump. Such traps act assentially as check valves which permit vapor flow only from the system to the pump and which prevent reverse or backstreaming flow.

Historically, the first use of such isolation traps began approximately 50 years ago. The principal types of isolation traps were refrigerated to operate at temperatures wherein the vapor pressure of a condensed pump fluid vapor would be very low, but wherein non-condensates (e.g. air) could pass freely from the system through the trap to the pump. Depending upon the degree of vacuum desired in the evacuated system, the temperatures within such refrigerated isolation traps typically were maintained as low as -1-95 C. (through the use of traps cooled by liquid nitrogen). The use of refrigerated traps immediately presents the problem of maintenance of the low temperature required by the trap. Temperature maintenance must necessarily be on a twenty-four hour a day, seven days a wee-k schedule.

3,426,511 Patented Feb. 11, 1969 A parallel approach to the use of refrigerated isolation traps, in accordance with the prior art, was to evacuate a system with pumps to a predetermined preliminary level. The system would then be completely sealed off and the absorption properties of a number of materials, particularly clean metals, such as barium films (getters), would be located in the sealed-off system to reduce further the pressure in the system to the desired level.

In accordance with the prior art, traps capable of operation at room temperature have been constructed. One such trap is embodied in Patent 2,831,549, issued to Alpert, and assigned to the same assignee as this invention. The Alpert room temperature trap comprises the use of a getter metal, in particular copper, which absorbs sufiicient quantities of pump vapor at room temperatures to permit the obtaining of ultra-high. vacuum conditions. The Alpert traps utilize a large effective surface area of clean copper metal. However, such traps are not scalable; that is, while copper traps are workable with small vacuum systems, they are not applicable for use with large, high conducting, ultra-high vacuum systems. In addition copper traps cannot maintain an ultra-high vacuum on systems for extended time periods.

In view of the foregoing, an object of the present invention is to provide a novel and efficient isolation trap.

Another object of the invention is the provision of an unrefrigerated isolation trap adapted for use in an ultrahigh vacuum system wherein pressures of 10- mm. mercury or less are maintained on the ultra-high vacuum side of the trap.

Further objects of the invention are to provide in an isolation trap means for increasing the conductance thereof while at the same time, increasing the effective life of the trap or greatly prolonging the interval between reconditionings thereof.

Another object of the invention is the provision of an isolation trap having means for supporting and utilizing sorption material in a novel manner.

,More particularly, it is an object of the invention to provide an isolation trap arranged so that the back streaming products of the pumps are caused to impinge directly against the surface of the sorption material without introducing a material pressure drop within the ultrahigh vacuum system.

An important object of the invention is the provision of a trap of the character described adapted particularly to utilize heretofore unknown sorption characteristics of certain materials under vacuum conditions.

These and other objects, features and advantages of the invention will be made apparent during the forthcoming description of illustrative embodiments of the invention, with the description being taken in conjunction with the accompanying drawings wherein:

FIGURE 1 is a longitudinally sectioned view of a portion of a high vacuum system incorporating a novel isolation trap of the invention;

FIG. 2 is a cross-sectional View of the isolation trap of FIG. 1 taken along reference lines II-II thereof;

FIG. 3 is a longitudinally sectioned view of another form of an isolation trap constructed in accordance with the invention;

FIG. 4 is a cross sectional view of the isolation trap of FIG. 3 taken along reference lines 1VIV thereof; and

FIG. 5 is a schematic view of an illustrative high vacuum system showing an exemplary application of the isolation trap depicted in FIGS. 3 and 4.

In accordance with the invention, a number of exemplary forms of unrefrigerated isolation traps are disclosed herein. These traps are provided pursuant to the invention with relatively large through conductances and therefore introduce very little pressure drop into the ultra-high vacuum system. Although ordinary bed materials can be used to some advantage in the isolation traps disclosed herein under refrigerated conditions, these traps are particularly adapted for use in non-refrigerated applications with certain materials exhibiting unusual and hereto unknown isolation trap properties under very high or ulttra-high vacua.

Specifically these materials are anhydrous alkali or alkaline earth metal alumino-silicates, more commonly known as zeolites. The more common, naturally occurring zeolites are denoted generally herein by the formulae:

where X denotes an alkali metal and Y denotes an alkaline earth metal.

The zeolites are naturally occurring minerals with waters of crystallization varying between 2 and 8 molecules and higher. The crystallizational water is easily released upon the application of heat and the zeolites intumesce during such heating to form a very porous structure. It is in their porous, anhydrous forms that the zeolites are employed in the isolation trap of the invention. As indicated previously, the desired porosity of these materials is obtained simply by driving off their waters of crystallization. It is not precisely known what part of the porous structure plays in the sorption capabilities of these materials since in many cases the pores thereof are too small to admit long-chain molecules.

In addition it will be appreciated that anhydrous forms of artificially produced alkali or alkaline earth metal alumino-silicates perform satisfactorily as bed materials for non-refrigerated isolation traps.

The porosity of these materials is believed to be a factor in their phenomenal sorption capabilities at extremely low pressures. However, the exact mechanism whereby sorption takes place in these materials is not clearly understood and may be a combination of both absorption, adsorption, and related processes. Nevertheless it now appears that the aforementioned anhydrous materials are capable of attracting, at extremely low pressures, many monolayers (probably in the order of 100) of back streaming molecules at their surfaces. In case of known sorption materials employed in ultra-high vacua, only a few monolayers of molecules are thus attracted, possibly in the order of ten or less. Also, there are certain sorption characterstics of these anhydrous materials which foster the belief that long chain molecules, constituting the greater proportion of the backstreaming products in the case where oil diffusion pumps are employed, may be attracted endwise to the surface of the sorption material. If such is actually the case, it would account in a very large measure for the tremendous sorption ability of the aforementioned materials. For example, there is some evidence indicating that the sorption capabilities of these materials are greater for unsaturated hydro-carbons, and thus, polar attraction may be a factor.

In the practice of the inventon, it has been found that the alakli-alumino-silicate species of zeolites activated by sintering to obtain anhydrous forms can be employed to considerable advantage. In particular, the sodiumor soda-alumino-silicates having the following formulae:

0.83 iODSNa O.l.OOAl O .2.48iO.03SiO 0.96:O.04Na O.l.OOAl O .1.92iO.09SiO in which the oxides are expressed in ratio to A1 taken as unity are desirable. These zeolites correspond repectively to anhydrous forms of he naturally pp g minerals analcite and natrolite. It is to be understood, however, that the sodium can be replaced by potassium or other metal of the alkali series. It is also contemplated that the zeolite can include other metals, for example an alkaline earth metal such as calcium, barium, strontium, or magnesium either in addition to or in replacement of the alkali metal as indicated by the general Formula 2 or 3. Examples of the latter groups of zeolites are as follows:

ChabaziteCaAl Si O (6) ScoleciteCaAl Si O (7) HeulanditeCa(Na O) .Al O .6SiO (8) StilbiteNa .CaO.Al O .6Si0 (9) HarmotoneK BaAl Si O (10) Formula 6 to 10, inclusive, likewise are anhydrous forms, corresponding to the minerals indicated above.

In accordance with the invention an isolation trap is structurally arranged so that the backstreaming products are caused to assume a tortuous path through the trap so that no line-of-sight passage is afforded thereto. Consequently, the backstreaming products are caused to impinge directly against exposed surfaces of the sorption material. However, as shown hereinafter, it is not necessary to closely confine the passage of the backstreaming products through the sorption material in order to facilitate attraction by the material. Consequently, very little pressure drop is introduced into the ultra-high vacuum system by the presence of the isolation trap.

Referring now more particularly to FIGS. 1 and 2 of the drawings, the exemplary form of the invention depicted therein comprises a vessel 10 to which is joined in this example a central inlet conduit 12 and an eccentric outlet conduit 14. Each of the conduits 12 or 14 is provided at its outward terminus with a flange 16 or 18, respectively. With the flange 16 or 18 the isolation trap 8 can be hermetically sealed to component parts of the vacuum system, as by annularly seal welding the flange 16 or 118 to a similar flange secured to the aforesaid components. In one application of the isolation trap 8 the flange 16 and conduit 12 are adapted to be joined to a similar conduit of a vessel or other container, which is adapted to be evacuated to an extremely low presssure. On the other hand, the flange 18 and conduit 14 are arranged for coupling to a similar conduit of a suitable pumping means, for example, the fore pumps and oil diffusion pump described previously. In the latter arrangement then the backstreaming products from the pumps will flow into the isolation trap 8 in the direction denoted by arrow 20.

In the present arrangement of the invention the central or inlet conduit 12 is extended for a distance into the vessel 10 and thus terminates in the central portion of the vessel in a flange member 22. A continuous weir member 24 surrounds the outer periphery of the flange 22 and is secured to the upper surface thereof. With this arrangement the flange 22 forms an open annular container or bed for a quantity of one of the aforementioned sorption materials, as denoted by reference character 26. The conduit 12 is joined and secured to the vessel 10 at its port of entry therein by means of fusion or welding as denoted by the reference character 28. This arrangement also forms a henmetic seal between the conduit 12 and the vessel 10. If desired, the conduit 14 can be formed integrally with the vessel 10.

A bed of a similar quantity 30 of the aforesaid sorption material is supported upon bottom wall 32 of the vessel 10. In this example, the bottom wall 32 is a spherical section in order to maximize the strength thereof relative to external ambient pressures.

It will be seen from FIGS. 1 and 2 that the dimensions of the trap are selected such that the trap 8 has a substantially greater conductance than that of the conduits 12 and 14 leading to and from the trap. As denoted previously, backstreaming products from the pumps enter the trap 8 as denoted by the arrow 20, thence a portion of the backstreaming products impinge upon the upper portion 26 of the sorption material as denoted by flow arrows 34. As shown in FIG. 1 these products are directed at the sorption material 26 and desirably at a fairly steep angle to the surface thereof which has been found in certain applications to aid in attracting the molecules of the backstreaming products to the sorption material.

Another portion of the backstreaming molecules flows through the annular space between the weir 24 and side wall 36 of the vessel as indicated by flow 38. The latter portion of the backstreaming molecules, together with any molecules not absorbed by the upper portion 26 of the sorption material, is directed substantially perpendicularly against the exposed surfaces of the lower portion of sorption material 30. Throughout the effective life of the isolation trap 8, virtually none of these backstreaming molecules reaches the inner opening 40 of the conduit 12, and thus the backstreaming products are effectively screened or isolated from the ultra-high vacuum system which is joined to the other extremity of the conduit 12. The air or other fluid removed from the aforesaid ultra-high vacuum system, of course, enters the trap as denoted by flow arrow 42, whence it passes to the outlet conduit 14 through the opening 40 and annular space 44 and leaves the trap 8 as denoted by flow arrow 43. As intimated above the width of the annular space 44 and the distance 46 between the bottom sunface of the flange 22 and the upper surface of the lower portion 30 of sorption material are selected such that the pressure drop induced thereby is less than that of a straight length of tubing corresponding to the conduits 12 or 14.

In one arrangement of the invention suitable, for a laboratory ultra-high vacuum system, the vessel 10 and the conduits or leads 12 and 14 were fabricated from Pyrex glass having a diameter of about 14 mm. The internal volume of the vessel was about one liter and the conductance of the leads about 0.3 liter/sec. per meter of length. The upper and lower beds of sorption material 26 and 30 each included a quantity of artificial zeolite pellets approximately 4; inch in diameter. The

pellets are anhydrous and are made porous by eliminating the water of crystallization from the zeolite material, which in this example has the chemical Formula 4. In addition to the sorption capabilities of the zeolite mate rial, its porous structure provides a very long path to retard the migration of impurities through the isolation trap.

The isolation trap 50 and related components as mentioned more fully hereinafter in connection with FIG. 5 of the drawings, were baked for 8 hours at 450 0., although the aforementioned zeolite material is reported to have a stable structure in its anhydrous form to 600 C.

With the isolation trap connected to an ultra-high vacuum system and to the oil-diflusion and fore pumps mentioned previously, the system was operated to maintain a pressure of about 1X10" mm. mercury. The system was able to maintain this extremely low pressure throughout durations of tests greater than 70 days with the above mentioned zeolite material or over 100 days with activated alumina. On the other hand, the most satisfactory of known unrefrigerated isolation traps when tested in this identical fashion remained effective for an average of only about 20 days, following which the pressure in the system rose to about 10' mm. mercury in a few days time. It should be mentioned further that the isolation trap 8 was able to attain this excellent performance without reducing the conductance thereof to a very low value.

Referring now to FIGS. 3 and 4 of the drawings, another form of the isolation trap of the invention is depicted therein. The latter arrangement is adapted particularly for the use with large-ultra-high vacuum systems requiring isolation traps of relatively high conductance.

The isolation trap 50 of FIGS. 3 and 4 is adapted for use with one or more of the anhydrous sorption materials discussed previously. In furtherance of this purpose the isolation trap 50 includes a housing 52 of generally cylindrical configuration having a pair of mounting flanges 54 and 56 are each provided with a plurality of bolt openings 58 whereby the flanges 54 and 56 can be joined and sealed to corresponding parts of other components of the high vacuum system, in a well known manner.

A number of beds of sorption material, with three such beds 60, 62 and 64 being employed in this example, are supported internally of the housing 52. However, as will be shown presently, a lesser or greater number of beds 60, 62 and 64 can be employed depending upon the size and the particular application of the isolation trap 50.

Each of the beds 60, 62 and 64 is combined with a flow bafile member. Thus, the sorption material of the bed 60 is supported within a relatively short cylindrical member 66, the lower extremity of which is closed by bottom wall 68 to contain the sorption material 60. The cylindrical member 66, however, is spaced inwardly of the housing 52 to form an annular flow passage 70 therebetween. At this position the cylindrical baffle 66 supported within the housing 52 by a plurality of fingers or spokes 72, with four being employed in this arrangement of the invention as better shown in FIG. 4.

The bed of sorption material 62 is supported intermediately of the housing 52 upon an annular plate 74 joined at its outer periphery to the inner wall of the housing 52, as by welding. A second cylindrical baflie 76 extends through the opening of the annular plate 74 and is disposed substantially perpendicularly thereto. For reasons hereinafter :made more apparent, the lower extremity 78 of the cylindrical bafile 76 extends a short distance into the upper end 80 of the first-mentioned cylindrical bafile 66. Similarly, the upper extremity 82 of the baffle 76 extends a short distance into the uppermost cylindrical baffle 84 presently to be described. The in terior of the cylindrical baffle 76 is unobstructed to provide a flow path through the isolation trap. For the same purpose, the bafiie member 76 is smaller in diameter than the cylindrical battles 66 and 84 so that unobstructed annular flow passages 86 and 88 are provided between the extremities 78 and 82, respectively of the bafile 76.

Adjacent the upper end of the housing 52 a third cylindrical bafile member 84 is positioned. The baflie 84 likewise is spaced inwardly of the housing 52 in order to form an annular flow passage 90 therebetween. The bafile 84 is joined at its upper extremity 92 to the inner surface of the housing 52 by a plurality of fingers or spokes 94. The spokes 94 are similar to the spokes 72 described heretofore and both groups of these members are joined to their respective parts, for example, by welding.

Intermediate the ends of the cylindrical baffle 84 a generally circular supporting plate 96 is secured at its outer periphery to the inner wall surface of the bafi le 84. The plate 96 is adapted to support the bed of sorption material 64, described above.

Finally, at the upper end of the housing 52, flanged baffle member 98 is positioned. The baffle 98 includes a relatively short, cylindrical member 100, which is joined at its upper extremity to an annular supporting plate 102. The supporting plate 102 is joined at its outer edge to the inner Wall surface of the housing 52 such that the lower extremity 104 of the cylinder extends a short distance into the upper extremity 92 of the cylindrical baffle 84. The cylinder 100 is spaced inwardly of the cylinder 84 and so defines an annular passage 106 therebetween. As in the case of the aforedescribed cylindrical batfie 76, the interior of the cylinder 100 is substantially unobstructed in order to provide a flow passage 108 there through.

For ease in manufacture and assembly it is desirable to form the cylindrical members 76 and 100 with the same diameter and wall thickness and likewise the cylindrical members 66 and 84. Consequently, the sizes of the annular flow passages 86, 88 and 106 will be equal and also the annular passages 70 and 90. Similarly, the configurations of the supporting plate 68 and 96 will be identical. In the embodiment of the invention shown in FIGS. 3 and 4, the cylindrical portions 66, 76, 84 and 100 have been shown and described as right circular cylinders.

However, it is contemplated that any other tubuli form members can be employed in their stead as long as the necessary flow passages 70, 86, 88, 90 and 106 remain. Depending upon the application desired and space requirements and the like, the housing 52 and the aforesaid cylindrical :members can be provided instead in the form of relatively flat tubular members (not shown).

In the arrangement shown in FIGS. 3 and 4, the housing 52, the baffle members 66, 76, 84, and 98 and the aforedescribed supporting members are fabricated from stainless steel. The housing 52 can be heliarc welded to the flanges 54 and 56 likewise fabricated from stainless steel. The sorption material 60, 62 and 64 in this example is the same as that described previously in connection with FIGS. 1 and 2. For convenience, the diameter of the housing 52 is made the same as that of the diffusion pump.

The isolation trap 50 is coupled to the remainder of the high vacuum system by providing each flange 54 and 56 with a step-seal arrangement. In furtherance of this purpose, each flange 54 or 56 is provided on its outward surface with an offset portion 110 in which is seated a copper gasket (not shown).

Referring now to FIG. 5, the aforementioned copper gasket is compressed between the flange 54 or 56 and a similar flange 112 secured to related components of the ultra-high vacuum system. To assist in monitoring the pressures of the system an ionization gauge denoted generally by the reference character 114 desirably is permanently secured to the system at the ultra-high vacuum side of the isolation trap. The trap 50 and the gauge 114 desirably are installed within a bakeout oven denoted generally by the dashed lines 116 for the purpose of periodically degassing the gauge and reconditioning the isolation trap while on system. The trap 50 is coupled at its ends to connecting conduits 118 and 120, respectively, which extend through appropriate walls of the bakeout oven 1.16. The upper connecting conduit 12% is joined to a vessel or container intended to be evacuated and indi cated generally by the reference character 122. The other connecting conduit 118 is joined to a water-cooled baffle denoted generally by the numeral 124 and in turn connected to the inlet of a water-cooled diffusion pump 126. The outlet 128 of the diffusion pump in turn is connected to the inlet port 130 of a fore pump (not shown).

In the high vacuum arrangement as shown in FIG. backstreaming products from the diffusion pump 126 and the aforesaid fore pump enter the isolation trap 50 and proceed therethrough as denoted by flow arrows 132. Accordingly, the backstreaming products pass through the annular flow passage 70 at the lower end of the housing 52 and are deflected from the undersurface of the annular supporting plate 74 from which they are guided downwardly by the cylindrical baffle 76 to impinge at an angle and desirably substantially perpendicularly upon the surface of the lowermost sorption bed 60. A fairly steep angle of impingement is desirable particularly where, as here, the bed has an appreciable depth. The nonabsorbed molecules of the backstreaming products then proceed upwardly through the circular passage 134 defined by the cylindrical baflie 76.

After leaving the baffle 76 the backstreaming products are again deflected and guided downwardly by the undersurface of the supporting plate 6 and the inner lower wall portion 136 of the cylindrical baffle 84. Again the back-streaming molecules impinge substantially perpendicularly against the surface of the intermediate sorption bed 62. After leaving the bed 62 the remaining backstreaming particles, if any, travel upwardly through the annular flow passage to the uppermost flanged baffle 98 where they are again reversed approximately by the mechanism described previously, to impinge substantially perpendicularly against the surface of the uppermost sorption bed 64. In this manner the backstreaming impurities are caused to assume a tortuous path through the isolation trap 50 and to impinge repeatedly upon the sorption material contained therein. As a result virtually none of the backstreaming products of the pumps or other impurities enters the inlet port 168 of the isolation trap.

Obviously, other materials than those described previously can be employed respectively in the sorption beds 60, 62 and 64. Such materials can be specifics, if desired, for certain oil vapors, decomposition products, or other impurities constituting the backstreaming products. These materials must, of course, be able to withstand high temperature, be degassable, and exhibit the sorption characteristics mentioned previously. For example spongy metal can be used to advantage in certain applications. It follows, of course, that two or more of any of the aforesaid compounds can be admixed to constitute one or more of the sorption beds 60, 62 or 64.

Although the isolation trap 50 is shown to be approximately the same diameter as that of the diffusion pump 126, the trap can readily be enlarged so that the annular passages 70, 86, 88, 90 and 166 thereof, and the openings through the cylindrical members 76 and 98 will have substantially the same conductance as that of the pump 126 and other components of the high vacuum system. With the latter arrangement, then, very little pressure drop is introduced into the system b the isolation trap.

In testing the isolation trap 50 with the arrangement depicted in FIG. 5 of the drawings, the area inside the dashed lines 116 was baked at 430 C. for 12 hours. The system was then operated and the pressure fell to less than the 1X10 mm. Hg, which is the X-ray limit of the ionization gauge 114. The pressure then remained, for repeated tests, at less than 5 l0" mm. Hg for 20 days. A larger model having a conductance of about 300 liters/ sec. maintained a pressure of 5 l0- mm. of Hg for 70 days. In contrast the most efficient of known unrefrigerated isolation traps was only capable, under these conditions, of maintaining isolation of the ultra-high vacuum system from backstreaming products of the pumps for less than one day.

If desired the entire inner surface of the housings l0 and 52 of traps 8 and 50, respectively are covered with a coating of a zeolite such as described heretofore. In the present example the zeolite material mentioned specifically in connection with FIG. 1 can be employed.

Such coatings can be applied, for example, by spraying an aqueous slurry of the zeolite and a binder clay upon the surfaces to be coated. The mixture of the sorption material and clay would then bind itself to the surfaces when the isolation trap is baked at the temperatures indicated previously. At the same time, of course, the sorption material would assume a very porous structure as the result of eliminating its water of crystallization.

It is apparent from the examples given that many different compounds may be utilized as sorption materials in the practice of a present invention. While, for purposes of this specification, zeolites have been defined herein as alkali or alkaline earth metal alumino-silicates, it must be appreicated that new synthetic zeolites referred to herein are constantly being developed and made commercially available, many of which undoubtedly will be found adaptable as sorption materials for the isolation traps described herein. To be eflective such new materials must have a sufficiently low vapor pressure to cause them to remain stable at the very high vacuum conditions and at the non-refrigerated conditions contemplated herein. It is therefore not only impossible to attempt a comprehensive catalog of useful sorption compounds but to attempt to apprehend or describe this feature of the invention in its broader aspects in terms of the chemical names of the compounds used would be misleading. This feature of the invention concerns the discovery of certain characteristics of compounds under ultra-high vacuum conditions as related to certain other physical characteristics of the compounds. The individual compositions of the compounds are important only in a sense that the individual properties of the elements of any mechanical assemblage are important to their proper combination and coaction. To formulate a set of specifications for specific sorption compounds in the light of the present disclosure will call for chemical knowledge and skill, but the oflice of the chemist wil be like that of the mechanical engineer who prescribes in the construction of a machine the proper materials and the proper dimensions therefor. From his knowledge as a chemist of the materials available he will know or deduce with confidence their applicability to the purposes of the invention or, otherwise, and in the case of novel materials routine tests not of an inventive nature will provide reliable data. In analogy to the case of a machine wherein the use of certain materials of construction or dimensions of parts would lead to no practically useful result, various materials will be rejected as inapplicable while others operative as such and illustrative of the theoretical basis of the invention may not be practically useful because the significant temperatures or ranges of temperatures involved would not be particularly advantageous or find a particular application in the prac} tical arts of consideration of the materials and the like. It may be safely assumed that no one will wish to employ a useless compound for the intended purposes or will be misled because it is possible to misapply the teachings of the present diclosure in order to do so.

From the foregoing, it will be apparent that novel and useful forms of unrefrigerated isolation traps have been disclosed herein. Numerous modifications of the invention will occur to those skilled in the art without departing from the spirit and scope of the invention. For example, there is evidence that an isolation trap provided with only one of the sorption beds shown in the drawings may be adequate to maintain pressures in the 1 10- to 10* range and that additional beds prolong the life of the trap. It is to be understood further that certain features of the invention can be employed without a corresponding use of other features thereof. Accordingly, it is intended that the illustrative and descriptive materials employed herein be used to illustrate the principles of the invention and not to limit the scope thereof.

I claim as my invention:

1. An isolation trap adapted for use in a high vacuumt system, said trap comprising a housing having inlet and outlet openings, a first bed of sorption material disposed with said housing adjacent the bottom thereof, an annular second bed of sorption material, means for supporting said second bed within said housing and spaced from said first bed and from the wall of said vessel so that said spacing is at least equivalent to each of said openings, a conduit supported within said vessel and connecting one of said openings with the aperture of said annular bed, said conduit communicating with the other of said vessel openings through the space between said beds and through the space between said second bed and said vessel wall, means for conducting a fluid entering said vessel though said other opening to one of said beds, and means for conducting that portion of said fluid not retained by said one bed to the other of said beds.

2. An isolation trap adapted for use in high vacuum systems, said trap comprising a housing having inlet and outlet openings, a first bed of sorption material supported within said housing adjacent an end thereof, said bed being spaced inwardly of said housing, a tubular flow baflle joined to the outer periphery of said bed and spaced inwardly of said housing to form an annular flow passage disposed between said battle and said housing and communicating with one of said housing openings, an annular second sorption bed supported withing said housing and spaced from said first bed, a second tubular baflle member extending through the opening in said annular bed, said second bafile member having at least the adjacent end potrion thereof of smaller cross section than that of said first-mentioned baifile member, said end portion extending into said first bafiie member to define a tortuous flow path through said housing and to cause said fluid to impinge substantially directly upon the surface of said first sorption bed, and third baflle means communicating with the other of said housing openings and disposed adjacent said second bafil'e member to cause said fluid to impinge substantially directly upon the surface of said second sorption bed.

3. The isolation trap of claim 2 wherein said third baffle means includes a tubular baflle member having at least an end portion of larger cross section than that of the other end portion of said second tubular baflle, said other end portion projecting into said third baflle means to define a tortuous path adjacent thereto and to cause said fluid to impinge directly upon the surface of said second sorption bed, and said third baffle means being spaced inwardly of said housing to form an annular flow passage communicating with said other housing opening.

4. The isolation trap of claim 2 wherein said beds contain a material selected from the group consisting of anhydrous zeolite compounds.

5. The isolation trap of claim 2 wherein at least the end portion of said third baflle means is larger in cross section than said other end of said second bafile member with said other end being inserted into said third bafile end portion to provide a tortuous flow path adjacent said other end and to cause said fluid to impingesubstantially directly upon the surface of said second sorption bed, and a third sorption bed supported within said third baflle member, and fourth bafile means supported within said housing for conducting said fluid directly against the surface of said third sorption bed.

6. The isolation trap of claim 5 wherein said fourth bafl le means includes an annular plate mounted within said housing adjacent the other end thereof, said plate overlying and being spaced from the adjacent opening of the annular space between said third baffle means and the Wall of said housing and a fifth tubular baffie member joined to the inner periphery of said annular palte and communicating through the opening thereof, with the other of said housing openings, said fifth tubular baflle member having at least the end portion thereof of smaller cross section than that of the adjacent end of said third basfile means and being inserted therein to provide a tortuous flow path adjacent said third baffle end and to cause said fluid to impinge directly against the surface of said third sorption bed.

7. An isolation trap adapted for use in high vacuum systems, said trap comprising an elongated housing having inlet and outlet openings therein, a plurality of beds of sorption material mounted in a spaced array along the length of said housing, alternate ones of said sorption beds being spaced inwardly from the walls of said housing to provide annular flow passages between said alternate beds respectively and the inner wall of said housing, the remainder of said beds being joined to the wall of said housing and being of annular configuration to form a central flow passage therethrough, and baflle means mounted within said housing and communicating with said housing openings for causing fluid entering said housing to assume a tortuous path through said annular and said central openings and to impinge substantially directly upon the surfaces of each of said sorption beds, said baflle means including a plurality of tubular baflle members, some of said baffie members being of relatively larger cross section and being joined to the outer peripheries respectively of said alternate beds, the remainder of said baflle members being of relatively smaller cross section and being joined to said remainder of the sorption beds at the inner periphery thereof, the ends of said baffle members being interfitted to provide said tortuous flow path through said housing.

8. The isolation trap of claim 7 wherein said housing is generally cylindrical and wherein said sorption beds are mounted in spaced relation along the length of said cylindrical housing and are disposed transversely thereof, wherein said alternate inwardly spaced ones of said beds are of substantially circular configuration, wherein said remainder of said beds defined a substantially circular central flow passage therethrough, said trap including an additional tubular baifile member supported adjacent the end of the flow path through said housing and commnicating with said outlet opening, said some tubular baflie members being of the same relatively large diameter, and said remainder of said bafile members including said additional baffle member being of the same relatively smaller diameter.

References Cited UNITED STATES PATENTS Patrick et al 5576 X Schaffer 55208 Jaycox 55208 X Hipple 55267 Alpert 230-69 Milton 5575 X Doying 55387 X Breck et al 5575 Great Britain.

15 REUBEN FRIEDMAN, Primary Examiner.

JOHN ADEE, Assistant Examiner. 

